Residual-Flexibility Corrections for Transient Modal Rotordynamic Models

1978 ◽  
Vol 100 (2) ◽  
pp. 251-256 ◽  
Author(s):  
D. W. Childs ◽  
J. B. Bates
Keyword(s):  
Space Shuttle ◽  
Power Level ◽  
Computer Time ◽  
Operating Speed ◽  
Flexible Rotors ◽  
Modes Of Vibration ◽  
Time Requirements ◽  
Reaction Forces ◽  
Bearing Stiffness ◽  
High Pressure Oxygen

An extension is presented to a modal formulation for the dynamics of flexible rotors. To date, rotordynamic modal formulations have retained for integration those modes of vibration whose natural frequencies are within or slightly above the operating speed range of the rotor, with higher-order modes simply discarded. In this study, the residual-flexibility technique is employed to account for the “static” contribution of these higher-frequency modes without requiring their integration. The residual-flexibility technique accounts directly for the static contribution of higher frequency modes due to imbalance and external transient loading, and has been adapted to account for reaction forces which are not accounted for by the nominal rotor/bearing stiffness matrix, e.g., bearing damping forces or speed-dependent bearing stiffnesses. The High-Pressure-Oxygen Turbopump of the Space Shuttle Main Engine (SSME) is analyzed. The maximum operating speed of this turbopump lies between its first and second critical speeds. Comparisons are made without residual-flexibility corrections for two through six modes retained for integration. Simulation runs are made for (a) a deceleration through the first critical speed and (b) a constant speed run at FPL (full power level). The results demonstrate that the residual-flexibility approach yields a significant improvement in accuracy for a comparatively modest increase in computer-time requirements.

Improved Rotor Response of the Uprated High Pressure Oxygen Turbopump for the Space Shuttle Main Engine

1989 ◽  
Vol 111 (2) ◽  
pp. 163-169 ◽  
Author(s):  
R. F. Beatty ◽  
M. J. Hine
Keyword(s):  
High Pressure ◽  
Critical Speed ◽  
Space Shuttle ◽  
Pressure Oxygen ◽  
Bearing Life ◽  
Bending Mode ◽  
Bearing Stiffness ◽  
High Pressure Oxygen ◽  
Bearing Loads ◽  
Main Engine

During development testing of the High Pressure Oxygen Turbopump (HPOTP) of the Space Shuttle Main Engine (SSME) to produce 109 percent of the rated thrust level, subsynchronous rotor whirl was encountered. This whirl was attributed to bearing wear reducing the radial bearing stiffness that caused the rotor second bending mode critical speed to enter the operating speed range. To eliminate this whirl, the pump end bearing loads were reduced to increase bearing life and damping added between the rotor and housing. This was achieved by converting impeller annular seals into “damping” seals that react part of the applied load and also damp the rotor response. Furthermore, the second rotor critical speed was increased by the added stiffness of the seal conversion and stiffening the rotor shaft. The bearing load reduction was verified by strain gaging the pump end bearing support into a load cell. These strain gages also were used to directly measure bearing ball wear during engine tests.

scholarly journals Vibration Characteristics of the HPOTP (High-Pressure Oxygen Turbopump) of the SSME (Space Shuttle Main Engine)

1985 ◽  
Vol 107 (1) ◽  
pp. 152-159 ◽  
Author(s):  
D. W. Childs ◽  
D. S. Moyer
Keyword(s):  
Nonlinear Model ◽  
Space Shuttle ◽  
Power Level ◽  
Structural Dynamic ◽  
Basic Model ◽  
Synchronous Motion ◽  
High Pressure Oxygen ◽  
Bearing Loads ◽  
Gas Seals ◽  
Main Engine

A review is presented of various rotordynamic problems which have been encountered and eliminated in developing the current flight engines and of continuing subsynchronous problems which are being encountered in developing a 109 percent power level engine. The basic model for the HPOTP, including the structural dynamic model for the rotor and housing and component models for the liquid and gas seals, turbine-clearance excitation forces, and impeller-diffuser forces, are discussed. Results from a linear model are used to examine the synchronous response and stability characteristics of the HPOTP, examining bearing load and stability problems associated with the second critical speed. Various seal modifications are examined and shown to have favorable consequences with respect to bearing reactions and stability. Differences between linear and nonlinear model results are discussed and explained in terms of simple models. The transient nonlinear model is used to demonstrate forced subsynchronous motion similar to that observed in test data for models which are lightly damped but stable. The subsynchronous motion results from bearing clearance nonlinearities. Simulation results indicates that synchronous bearing loads can be reduced but that sub-synchronous motion is not eliminated by seal modifications.

Extended Finite Element Analysis of Journal Bearing Dynamic Forced Performance to Include Fluid Inertia Force Coefficients

2012 ◽  
Author(s):  
Luis San Andrés
Keyword(s):  
Finite Element ◽  
Test Data ◽  
Small Amplitude ◽  
Forced Response ◽  
Inertia Force ◽  
Fluid Inertia ◽  
Inertia Effects ◽  
Force Coefficients ◽  
Reaction Forces ◽  
Bearing Stiffness

Reynolds equation governs the generation of hydrodynamic pressure in oil lubricated fluid film bearings. The static and dynamic forced response of a bearing is obtained from integration of the film pressure on the bearing surface. For small amplitude journal motions, a linear analysis represents the fluid film bearing reaction forces as proportional to the journal center displacements and velocity components through four stiffness and four damping coefficients. These force coefficients are integrated into rotor-bearing system structural analysis for prediction of the system stability and the synchronous response to imbalance. Fluid inertia force coefficients, those relating reaction forces to journal center accelerations, are routinely ignored because most oil lubricated bearings operate at relatively low Reynolds numbers, i.e., under slow flow conditions. Modern rotating machinery operates at ever increasing surface speeds to deliver more power in smaller size units. Under these operating conditions fluid inertia effects need to be accounted for in the forced response of oil lubricated bearings, as recent experimental test data also reveal. The paper presents a finite element formulation to predict added mass coefficients in oil lubricated bearings by extending a basic formulation that already calculates the bearing stiffness and damping force coefficients. That is, a small amplitude perturbation analysis of the lubrication flow equations keeps the temporal fluid inertia effects and develops a set of equations to obtain the bearing stiffness, damping and inertia force coefficients. The method does not impose on the cost of the original formulation which makes it very attractive for ready implementation in existing software. Predictions of the computational model are benchmarked against archival test data for an oil-lubricated pressure dam bearing supporting large compressors. The comparisons show fluid inertia effects cannot be ignored for operation at high rotor speeds and with small static loads.

scholarly journals Investigation of Rotor Blade Roughness Effects on Turbine Performance

1992 ◽  
Author(s):  
J. L. Boynton ◽  
R. Tabibzadeh ◽  
S. T. Hudson
Keyword(s):  
Surface Finish ◽  
Space Shuttle ◽  
Power Level ◽  
Rotor Blades ◽  
Machining Process ◽  
Inlet Temperature ◽  
Test Results ◽  
Roughness Effects ◽  
Turbine Efficiency ◽  
Swirl Angle

The cold air test program was completed on the SSME (Space Shuttle Main Engine) HPFTP (High Pressure Fuel Turbopump) turbine with production nozzle vane rings and polished coated rotor blades with a smooth surface finish of 30 microinch (0.76 micrometer) RMS (Root Mean Square). The smooth blades were polished by an abrasive flow machining process. The test results were compared with the air test results from production rough coated rotor blades with a surface finish of up to 400 microinch (10.16 micrometer) RMS. Turbine efficiency was higher for the smooth blades over the entire range tested. Efficiency increased 2.1 percentage points at the SSME 104 percent RPL (Rated Power Level) condition. This efficiency improvement could reduce the SSME HPFTP turbine inlet temperature by 57 degrees Rankine (32 degrees Kelvin) increasing turbine durability. The turbine flow parameter increased and the mid-span outlet swirl angle became more axial with the smooth rotor blades.

scholarly journals A Magnetic Damper for First Mode Vibration Reduction in Multimass Flexible Rotors

1989 ◽  
Author(s):  
M. E. F. Kasarda ◽  
P. E. Allaire ◽  
R. R. Humphris ◽  
L. E. Barrett
Keyword(s):  
Vibration Reduction ◽  
Working Fluid ◽  
Test Rig ◽  
Flexible Rotors ◽  
Fluid Environment ◽  
Bearing Stiffness ◽  
Mode Vibration ◽  
Vibration Problems ◽  
Set Up ◽  
Stiffness And Damping

Many rotating machines such as compressors, turbines and pumps have long thin shafts with resulting vibration problems. They would benefit from additional damping near the center of the shaft. Magnetic dampers have the potential to be employed in these machines because they can operate in the working fluid environment unlike conventional bearings. This paper describes an experimental test rig which was set up with a long thin shaft and several masses to represent a flexible shaft machine. An active magnetic damper was placed in three locations: near the midspan, near one end disk, and close to the bearing. With typical control parameter settings, the midspan location reduced the first mode vibration 82%, the disk location reduced it 75% and the bearing location attained a 74% reduction. Magnetic damper stiffness and damping values used to obtain these reductions were only a few percent of the bearing stiffness and damping values. A theoretical model of both the rotor and the damper was developed and compared to the measured results. The agreement was good.

Controlling Vibration in Remote Manipulators

1987 ◽  
Author(s):  
N. C. Singer ◽  
W. P. Seering
Keyword(s):  
Space Shuttle ◽  
Feedforward Control ◽  
Vibration Reduction ◽  
Flexible Structures ◽  
Robotic Manipulators ◽  
Control Problems ◽  
Software Model ◽  
Modes Of Vibration ◽  
Vibrational Characteristics ◽  
Special Control

Abstract Robotic manipulators for use in space have flexible structures and as a result have special control problems. These manipulators change their vibrational characteristics as they change in orientation. The Space Shuttle Remote Manipulator System (RMS) was chosen as a typical system and experiments were performed using the Draper Laboratory software model of the arm (DRS). First, the workspace of the manipulator was characterized in terms of the robot’s first two modes of vibration. Next, some feedforward experiments were performed on the computer model to show the promise of vibration reduction using feedforward control.

Two Jeffcott-Based Modal Simulation Models for Flexible Rotating Equipment

1975 ◽  
Vol 97 (3) ◽  
pp. 1000-1014 ◽  
Author(s):  
Dara W. Childs
Keyword(s):  
Arbitrary Number ◽  
Space Shuttle ◽  
Simulation Models ◽  
Computer Time ◽  
Rigid Bodies ◽  
Simulation Approach ◽  
Flexible Rotor ◽  
Computationally Efficient ◽  
Efficient Simulation ◽  
Main Engine

Two transient modal simulation models are presented based on the Jeffcott-Green flexible-rotor formulation. One of the models is based on the conventional “non-spinning” formulation, while the second employs a rotor fixed formulation. Numerical results are presented for these two basic models for the SSME (Space Shuttle Main Engine) turbopumps. The results presented demonstrate that either of the basic formulations is a computationally efficient simulation approach for a flexible rotor, which is to be modeled by a large number of rigid bodies. They also demonstrate that the models can readily account for an arbitrary number of bearings having nonlinear or speed-dependent characteristics, and for the motion of the bearing support structure. The results presented demonstrate that the rotor-fixed formulation generally requires less computer time than does the conventional formulation. Moreover, the modal cordinate solutions in the rotor-fixed formulation provide a significantly clearer picture of potential flexible-rotor-instability problems.

Optimum Bearing and Support Damping for Unbalance Response and Stability of Rotating Machinery

1978 ◽  
Vol 100 (1) ◽  
pp. 89-94 ◽  
Author(s):  
L. E. Barrett ◽  
E. J. Gunter ◽  
P. E. Allaire
Keyword(s):  
Approximate Method ◽  
Critical Speed ◽  
Exact Methods ◽  
Mass Model ◽  
Unbalance Response ◽  
Flexible Rotors ◽  
Bearing Stiffness ◽  
Single Mass ◽  
Internal Rotor ◽  
Stability Limits

This paper presents a rapid approximate method for calculating the optimum bearing or support damping for multimass flexible rotors to minimize unbalance response and to maximize stability in the vicinity of the rotor first critical speed. A multimass rotor is represented by an equivalent single-mass model for purposes of the analysis. The optimum bearing damping is expressed as a function of the bearing stiffness and rotor modal stiffness at the rigid bearing critical speed. Stability limits for aerodynamic cross coupling and viscous internal rotor friction damping are also presented. Comparison of the optimum damping obtained by this approximate method with that obtained by full scale linearized transfer matrix methods for several rotor-bearing configurations shows good agreement. The method has the advantage of being quickly and easily applied and can reduce analysis time by eliminating a time consuming search for the approximate optimum damping using more exact methods.

scholarly journals Investigation of Rotor Blade Roughness Effects on Turbine Performance

1993 ◽  
Vol 115 (3) ◽  
pp. 614-620 ◽  
Author(s):  
J. L. Boynton ◽  
R. Tabibzadeh ◽  
S. T. Hudson
Keyword(s):  
Surface Finish ◽  
Space Shuttle ◽  
Power Level ◽  
Rotor Blades ◽  
Machining Process ◽  
Inlet Temperature ◽  
Test Results ◽  
Roughness Effects ◽  
Turbine Efficiency ◽  
Swirl Angle

The cold air test program was completed on the SSME (Space Shuttle Main Engine) HPFTP (High-Pressure Fuel Turbopump) turbine with production nozzle vane rings and polished coated rotor blades with a smooth surface finish of 30 μin. (0.76 μm) rms (root mean square). The smooth blades were polished by an abrasive flow machining process. The test results were compared with the air test results from production rough-coated rotor blades with a surface finish of up to 400 μin. (10.16 μm) rms. Turbine efficiency was higher for the smooth blades over the entire range tested. Efficiency increased 2.1 percentage points at the SSME 104 percent RPL (Rated Power Level) conditions. This efficiency improvement could reduce the SSME HPFTP turbine inlet temperature by 57 R (32 K), increasing turbine durability. The turbine flow parameter increased and the midspan outlet swirl angle became more axial with the smooth rotor blades.

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